Andrea McGhee – Chemical Communications Blog

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A supramolecular approach to zwitterionic metal silanides

31 Mar 2011

Zwitterionic metal silanides represent a structurally novel class of tri-coordinated silyl anions in which the cationic metal centre is separated from the silicon anion by internal donor bridges.

Clemens Krempner and co-workers have now reported that key to the synthesis of stable, isolable species is the use of pendant polydonor groups that exclusively bind to the metal cation and serve to prevent self-aggregation.

Due to the shape of these unusual compounds, the electron pair located at the central silicon anion is available for additional metal binding. This has allowed for the synthesis of hitherto unknown zwitterionic heterobimetallic silanides, by reaction of the zwitterionic metal silanides with boron, aluminium or tungsten-containing species.

To read about these intriguing compounds in more detail, download the ChemComm communication, which is available for free until April 28th.

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Catalytic reaction cascade forms substituted pyrroles

31 Mar 2011

Catalytic reaction cascades present a neat, efficient way to synthesise valuable organic molecules. However, their success relies upon the compatibilty of the reactants and catalysts involved, and identifying this requires ingenuity and experimentation.

Now Darren Dixon and co-workers at the University of Oxford have reported a one-pot nitro-Mannich/hydroamination cascade for direct synthesis of 2,5-disubstituted pyrroles from imines and nitro alkynes. The reaction is catalysed by base and a gold(I) catalyst, and has been optimised to achieve yields up to 86%.

To find out more download the ChemComm communication, which is free to access until April 28th

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Novel methodologies for synthesising pyroglutamates

04 Mar 2011

Several pyroglutamate-based natural products have been found to exhibit potent anti-cancer and anti-microbial properties. Although their syntheses have been a focus of research for many groups, their is still room for improvement in the development of highly tunable methodologies for the diverse functionalisation of the pyroglutamate ring.

Venkatram R. Mereddy and co-workers have developed a novel and exceptionally short methodology for the synthesis of such functionalised pyroglutamates via alkylation of amino acid-derived iminoesters with allyl bromides or allyl acetates, easily obtained by Bayliss-Hilman reaction.

To learn more download the ChemComm communication, available for free until March 28th

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Intramolecular cycloaddition leads to the pentacyclic core of cortistatins

28 Feb 2011

Synthesising intriguing bioactive natural products in the most expedient and atom-efficient manner remains a highly active and competitive field of research. Cortistatins A and J, first isolated from the marine sponge Corticium simplex in 2006, have been identified as effective anti-angiogenics, which studies have found could suppress cancer recurrence when given in conjunction with traditional cancer drugs.

Lok Lok Liu and Pauline Chiu at the University of Hong Kong have reported a concise, high yielding, asymmetric synthesis of the pentacyclic framework of the cortistatins, in 12 steps from commercially available starting materials. Their synthesis employs a highly diastereoselective intramolecular [4+3] cycloaddition of epoxy enolsilanes as the key step and brings them close to their ultimate goal.

To find out more, download the ChemComm communication for free up until March 28th

To start a discussion, leave your comments below and for a related blog post see the Totally Synthetic blog pages.

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Nanoflowers for protein immobilisation and separation

15 Feb 2011

It is the quest of many a materials scientist to form core-shell nanostructures by self-assembly, in order to generate materials with unique structures and functions. In this area, hierarchical nanoarchitectures assembled from nanoscale units have recently stimulated tremendous interest because these superstructures might avoid aggregation and maintain high specific surface areas. In addition, magnetic materials have received considerable interest, due to their ability to selectively capture target objects from complex mixtures.

Ken Cham-Fai Leung and colleagues – based in Hong Kong and Hefei, China – have reported a facile synthesis of monodispersed microparticles composed of superparamagnetic Fe₃O₄ cores, a SiO₂ shell and a hierarchical g-AlOOH periphery with Au nanoparticles, obtaining nanoflower structures resembling daisies. As proof of principle for their use as selective protein capturing agents, these nanoflowers were applied as absorbents to successfully remove bovine serum albumin from bovine blood.

To find out more download the ChemComm communication, which is free to access until 15th March 2011.

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Negishi cross-coupling using a bulky Pd-NHC catalyst

07 Feb 2011

The hugely important field of transition metal catalysed C–C cross-coupling has come a long way over the years, but efficient coupling between Csp² and secondary Csp³ centres remains a challenge. To achieve just that, Michael Organ and his colleague Selcuk Calimsiz (York University, Toronto) have developed and used a bulky Pd-NHC (N-heterocyclic carbene) catalyst called Pd-PEPPSI-IPent.

In the reactions of secondary alkylzincs with a variety aryl or heteroaryl halides, this catalyst provided excellent regioselectivity for the branched product over the isomerised unbranched product, far outperforming the less bulky Pd-PEPPSI-IPr analogue.

To see the impressive scope of the reaction download the ChemComm communication for free up until 7th March 2011 and leave your comments below.

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Proof-of-principle concept for label-free detection of glucose and alpha-glucosidase activity

28 Jan 2011

Glycogen storage disease type II (GSD II), also known as Pompe disease, is a genetic disorder that results in muscle and nerve cell damage caused by deficiency of the lysosomal acid a-glucosidase enzyme. In an effort to achieve a better technique for screening enzyme activity in patients suffering from Pompe disease, Prof. Vivian Yam and colleagues at the Institute of Molecular Functional Materials, University of Hong Kong, have synthesised a two-component platinum (II) complex-polymer ensemble for glucose sensing and a-glucosidase assay.

The system works by strongly binding glucose, resulting in a 46-fold increase in the low energy emission band (800 nm) of the electronic emission spectrum. Additionally, in the presence of a-glucosidase and maltose (which is broken down to glucose by a-glucosidase), the intensity of the 800 nm emission band was found to increase with time. These results provide a “proof-of-principle” concept for label-free detection of glucose and open the way for rapid and sensitive detection of a-glucosidase.

To find out more download the ChemComm communication for free until 25th February 2011.

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Lack of luminescence quenching does not prove DNA intercalation by Ru(II) complexes

21 Jan 2011

The binding of luminescent complexes to DNA is a popular area of research, with applications ranging from molecular switches to photodynamic therapy. It has commonly been reported in the literature that a lack of luminescence quenching by ferrocyanide, [Fe(CN)₆]⁴⁻, can be used as evidence of the intercalation of a complex with DNA.

Claudia Turro and colleagues at Ohio State University have now shown that a Ru(II) complex that binds strongly to DNA electrostatically rather than by intercalation is equally resistant to ³MLCT (metal-to-ligand charge transfer) emission quenching as one known to be a DNA intercalator.

These findings indicate that the absence of emission quenching by [Fe(CN)₆]⁴⁻cannot be used alone as proof of DNA intercalation by a complex. Hence, researchers using this method will need to take extra care when interpreting their results.

To find out more and start a discussion download the communication (for free until 18th Feb 2011) and leave your comments below.

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Chemical Communications Blog

Author Archive

A supramolecular approach to zwitterionic metal silanides

Catalytic reaction cascade forms substituted pyrroles

Novel methodologies for synthesising pyroglutamates

Intramolecular cycloaddition leads to the pentacyclic core of cortistatins

Nanoflowers for protein immobilisation and separation

Negishi cross-coupling using a bulky Pd-NHC catalyst

Proof-of-principle concept for label-free detection of glucose and alpha-glucosidase activity

Lack of luminescence quenching does not prove DNA intercalation by Ru(II) complexes

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